1. Field of the Invention
The present invention generally relates to a heat treatment method and apparatus and, more particularly, to a heat treatment method and apparatus for applying a heat treatment to various substrates such as, for example, a semiconductor wafer or a glass substrate for liquid crystal displays.
2. Description of the Related Art
There are various types of heat treatment apparatuses for performing an annealing process, which is one of semiconductor manufacturing processes. For example, a heat treatment apparatus of a single-wafer type such as shown in FIG. 1 is used as an apparatus used for, among annealing processes, a process for activating ions implanted in a polysilicon layer on a substrate surface. In FIG. 1, provided inside a heating furnace 1 is a reaction container 11, which is made from quartz and forms a processing atmosphere therein. A substrate placement part 12, which supports horizontally a semiconductor wafer (hereinafter referred to as a wafer) W as an object to be processed, is provided in the reaction container 11. An opening part 13 is formed on one side of the reaction container 11 of the heating furnace 1 for carrying in and out the wafer W, and a purge-gas supply pipe 14, which is connected to an interior of the reaction container 11, is provided on another side by being extended through the side wall of the heating furnace 1.
Additionally, heaters 15 (indicated by single-dashed chain lines) are provided to a ceiling part, a bottom part and side walls of the heating furnace 1 so as to surround the wafer W. A uniform-heating plate 16 is provided between the reaction container 11 and each of the heaters 15. The uniform-heating plate 16 is formed of a material such as silicon carbide (SiC) having a large heat capacity so as to diffuse heat generated by the heaters 15 and uniformly heat the entire substrate. A thermocouple 17 is provided outside the uniform-heating plate 16 so as to detect a temperature in the vicinity of the heaters 15. A value of a temperature detected by the thermocouple 17 is supplied to a control part 18 so as to adjust an amount of electric power supplied to the heaters 15 so that a surface temperature of the wafer W is maintained at a setting temperature. According to such a temperature control system, there is an advantage that a temperature control is easy.
However, in the heat treatment apparatus having the above-mentioned structure, when consecutively repeated operations are performed to carry wafers into the heating furnace 1 so as to process the wafers W and carry out the wafers W one after another, there is a problem in that the temperature inside the furnace at the time of processing the second sheet of wafers W becomes lower than the temperature at the time of processing the first sheet of wafers W. That is, although the cold wafer W carried into the reaction container 11 may reduce the temperature of the processing atmosphere inside the heating furnace 1, the temperature of the uniform-heating plate 16 hardly decreases due to its large heat capacity. For this reason, there is a delay in the detection of the temperature inside the reaction container 11 by the thermocouple 17, which is provided outside the uniform-heating plate 16, which results in that the temperature of the processing atmosphere cannot return to the setting temperature. Moreover, similarly in a heat treatment apparatus that does not have the uniform-heating plate 16, when a heat capacity of the reaction container is large, there is a delay in the detection of a temperature drop.
That is, the temperature inside the furnace cannot return to a predetermined process temperature since a response with respect to an external disturbance due to carry-in of wafers at an initial stage such as the time of carrying-in the first or second sheet of wafers. Moreover, since an increase in the wafer size has been progressed in recent years, the degree of cooling down inside the reaction container 11 becomes large at the time of carrying-in of the wafers. For the above-mentioned reasons, the temperature drop tends to be increased.
Specifically, in the example shown in FIG. 6 (a process temperature of 600xc2x0 C., a process time of 60 seconds, a carry-in and carry-out time of 120 seconds), the temperature of the processing atmosphere gradually decreases from the time of processing the first wafer to the time of processing the fifth wafer, and, thereafter, the temperature stays at a temperature lower than the process temperature by 25 degrees. The range of drop of the processing temperature seen from the process temperature tends to increase as a process time A1 (time interval) per one sheet of wafers shown in the figure is reduced. If the time interval is shorter than that in the case of FIG. 6, and is set to, for example, 60 seconds, the range of temperature drop may become quite remarkable.
Moreover, there is a baking process being performed using a heating plate as measures for solving the problem due to the cold wafers at the time of heat-treating the wafers. When performing such a baking process, a heater provided in the heating plate is driven at a maximum power each time an individual wafer is placed on the heating plate, and, then, switched to an automatic temperature control state. It is known that a time period of driving the heater at the maximum power is set to a time period which is sufficient for supplying an amount of heat corresponding to an amount of heat generated by the heating plate and absorbed by the wafers. Japanese Laid-Open Patent Application No. 11-74187 discloses such a technique. Similar to a baking process for a resist film by a heating plate (hot plate), in a case where a supply of heat to wafers sensitively responds to an electric power supply to the heater, a heat treatment can be uniformly applied to each wafer. However, when a member having a large heat capacity such as a reaction container or a uniform-heating plate is interposed between the heater and the wafer, the process temperature after the process of the second sheet of wafers cannot be always equal to the process temperature at the time of processing the first sheet of wafers. Accordingly, a uniform process cannot be applied to each wafer.
It is a general object of the present invention to provide an improved and useful heat treatment method and apparatus in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide a heat treatment method which can reduce a temperature drop when a plurality of objects to be processed are consecutively processed one after another so as to improve uniformity of process quality between the objects.
In order to achieve the above-mentioned objects, there is provided according to another aspect of the present invention a heat treatment method for continuously applying a heat treatment to a plurality of objects to be processed that are sequentially supplied to a reaction container, the heat treatment method using a heat treatment apparatus which heats the objects placed inside the reaction container by a heater provided outside the reaction container, the heat treatment method comprising the steps of: obtaining an offset temperature value which is a difference between a temperature of a processing atmosphere at a time immediately before a first one of the objects is carried into the reaction container and a temperature of the processing atmosphere at a time the temperature has become constant after the objects are subjected to a heat treatment process consecutively one after another; supplying an electric power to the heater so as to obtain a time period necessary for raising the temperature of the processing atmosphere to a temperature higher than a setting temperature for the heat treatment process by the offset temperature value; and supplying the electric power to the heater for only the time period obtained in the preceding step when the first one of the objects is carried into the reaction container, and, thereafter, performing an electric power control of the heater based on a temperature detection value of a temperature detecting part provided outside the reaction container.
There is provided according to another aspect of the present invention a heat treatment method for applying a heat treatment to a plurality of objects to be processed that are sequentially supplied to a reaction container, the heat treatment method using a heat treatment apparatus which heats the objects placed inside the reaction container consecutively one after another by a heater provided outside the reaction container at a process temperature, the heat treatment method comprising the steps of: obtaining a first relationship between a time interval and an offset temperature value, wherein the time interval is a period from a time when one of the objects is carried into the reaction container until a time when a subsequent one of the objects is carried into the reaction container and the offset temperature value is a difference between a temperature of a processing atmosphere at a time immediately before a first one of the objects is carried into the reaction container and a temperature of the processing atmosphere at a time the temperature has become constant after the objects are subjected to a heat treatment process consecutively one after another; supplying an electric power to the heater so as to raise the temperature of the processing atmosphere by the offset temperature value, and obtaining a second relationship between the offset temperature value and a time period during which the electric power has been supplied; obtaining a time period for supplying the electric power corresponding to the process temperature and the time interval based on the first relationship and the second relationship; and supplying the electric power to the heater for only the time period obtained in the preceding step when the first one of the objects is carried into the reaction container, and, thereafter, performing an electric power control of the heater based on a temperature detection value of a temperature detecting part provided outside the reaction container.
According to the heat treatment method of the present invention, before performing the electric power control (the regular electric power control) of the heater based on the temperature detection value from the temperature detection part provided outside the reaction container, the electric power is supplied to the heater for only a predetermined time so that the temperature of the processing atmosphere becomes higher than the process temperature. For this reason, for example, when consecutively performing a heat treatment on the objects to be processed, the offset temperature value can be compensated for and the process temperature to all the objects to be processed can be made uniform. Therefore, the uniformity of heat treatment between the objects to be processed is improved.
In the heat treatment method according to the present invention, a setting temperature for the electric power control of the heater performed after the electric power is supplied to the heater may correspond to a temperature calculated by adding the offset temperature value to the temperature for the heat treatment process. Additionally, the electric power may be supplied to the heater based on a control signal supplied from an outside of a feedback control loop using the temperature detection value. Further, a uniform-heating member, which serves to uniformly heat the reaction container, may be provided between the reaction container and the heater.
There is provided according to another aspect of the present invention a heat treatment apparatus for heating a plurality of objects to be processed consecutively one after another, the objects being placed inside a reaction container and heated by a heater provided outside the reaction container at a process temperature, the heat treatment apparatus comprising: a first memory part storing a first relationship between a time interval and an offset temperature value in relation to the process temperature, wherein the time interval is a period from a time when one of the objects is carried into the reaction container until a time when a subsequent one of the objects is carried into the reaction container and the offset temperature value is a difference between a temperature of a processing atmosphere within the reaction container at a time immediately before a first one of the objects is carried into the reaction container and a temperature of the processing atmosphere at a time the temperature has become constant after the objects are subjected to a heat treatment process consecutively one after another; a second memory part storing, in relation to the process temperature, a second relationship between the offset temperature value and a time period during which an electric power is supplied to the heater so as to raise the temperature of the processing atmosphere by the offset temperature value; means for obtaining a time period for supplying the electric power corresponding to the process temperature and the time interval based on the first relationship and the second relationship; a temperature detecting part provided outside the reaction container; and a control part supplying the electric power to the heater for only the time period obtained by the means when the first one of the objects is carried into the reaction container, and, thereafter, performing an electric power control of the heater based on a temperature detection value of the temperature detecting part.
The heat treatment apparatus according to the present invention may comprise a program for creating the first relationship and the second relationship. Additionally, the electric power may be supplied to the heater based on a control signal supplied from an outside of a feedback control loop using the temperature detection value. The heat treatment apparatus according to the present invention may further comprise a uniform-heating member, which serves to uniformly heat the reaction container and provided between the reaction container and the heater. Additionally, the objects to be processed may be substrates; a conveyance opening for the substrates may be provided on a side of the reaction container; and the heater may be configured and arranged to heat both sides of each substrate.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.